The long-range objective of this research is an understanding of the biochemical mechanisms that operate and regulate the expression of human genes during growth and differentiation. The human epidermis has been chosen as a model system, since we are able to serially cultivate these cells in vitro under conditions where many of the differentiative properties, including stratification are retained. The major differentiation-specific proteins in these cells are the keratins, a group of closely related proteins of MW 40-70 K daltons that form 80 A cytoskeletal filaments. Only a subset of these keratins are ever expressed by an epidermal cell at any one time. During the course of differentiation, this subset changes concomitantly with an increase in keratin synthesis, leaving the fully differentiated epidermal cell with 85% of its total protein as keratins. We already know that early changes in the differentiation involve changes in mRNA's whereas late changes involve proteolytic processing. We would now like to isolate cDNA clones to the different keratin mRNAs and use these probes to study the regulation of keratin mRNAs and hnRNAs during the early stages of differentiation. We will also determine the number of different keratin genes and whether their chromosomal organization can be related to their sequential appearance during cell maturation. The amino acid sequence of the four major keratins will be determined from the nucleic acid sequence of full-length cDNA clones. This will be of particular interest in elucidating the significance of the multiple keratin forms and their differential expression. Finally, epidermal cells from patients with genetic skin diseases and basal/squamous cell carcinomas will be cultured and alterations in the regulation/expression of the keratins and other differentiation-specific proteins in these cells will be investigated.